1. Field of the Invention
The invention relates to a fuel cell terminal plate that is used to collect power generated by a fuel cell through electrochemical reaction between hydrogen and oxygen, a method for manufacturing the plate, and a fuel cell incorporating the plate.
2. Description of the Related Art
Water is inevitably produced as power is generated through electrochemical reaction between hydrogen and oxygen at a fuel cell. In the case of a solid-electrolyte membrane type fuel cell, because the electrolyte membrane needs to be kept moistened, fuel gas is often supplied to the fuel cell together with water vapor. Further, in order to maintain the temperature of the fuel cell at a suitable temperature for the electrochemical reaction, coolant is circulated through the fuel cell. Thus, in each fuel cell unit as a power generation element of the fuel cell, separators that partition the fuel cell from the adjacent fuel cell units may contact, under the electric potential produced by the power generation of the fuel cell being applied thereto, the water produced by electrochemical reactions and the water contained in the gases. Therefore, the separators need to have both a high corrosion resistance and a low contact resistance. Further, the separators need to have a high corrosion resistance against corrosive elements dissolved in the produced water and the water in the gases, apart from the contact resistance against water under the electric potential mentioned above being applied. For these reasons, the surface of the separator of the fuel cell described in the Japanese Patent Application Publication No. 2001-345109 (JP-A-2001-345109) is applied with a gold-plating layer that has both high corrosion resistance and a low contact resistance.
The power generated by each fuel cell unit is collected via conductive terminal plates provided at the both ends of the fuel cell stack, which is constituted of a plurality of fuel cell units stacked on top of each other, and then outputted. Because the terminal plates collect power generated while serving also as portions via which fuel gases and coolant are distributed to and discharged from the respective fuel cell units, the corrosion resistance of the terminal plates needs to be as high as that of the separators, and the contact resistance of the terminal plates needs to be as low as that of the separators.
Used to collect the generated power, the terminal plates are exposed in a large electric potential difference, they require different measures from those for the separators. For example, in order to prevent the terminal plates from contacting the water in the gases distributed to and discharged from the respective fuel cell units and the coolant, conductive sealing plates are provided between the fuel cell units at the ends of the fuel cell stack and the respective terminal plates. Although the use of such sealing plates increases the contact resistance and thus slightly reduces the power output of the fuel cell stack, a higher priority is often given to secure a high corrosion resistance. For example, a high corrosion resistance and a low contact resistance of each terminal plate can be achieved by plating the entire surface of each terminal plate with gold. In this case, however, because gold is precious, the amount of gold used for such plating needs to be saved.